1. Field of the Invention
The present invention relates to an image inspection method, an image inspection apparatus, and a recording medium storing an image inspection control program, and more particularly to a method and an apparatus of inspecting a printed image.
2. Description of the Related Art
Conventionally, inspection of printed matter printed out by a printing apparatus is performed by human operators. In recent years, an inspection apparatus that automatically inspects printed matter has been used. In such an inspection apparatus, a master image serving as a reference image is generated by reading a base document prepared in advance, and corresponding portions of the master image and a read image of printed matter are compared to determine, by the degree of the difference therebetween, whether there is a defect in the printed matter.
The inspection target of the inspection apparatus is not limited to printed matter where the same content is printed each time. For instance, the inspection target may be a large number of printed documents that respectively have different contents, such as a large number of statements or bills printed for numerous customers. For a method of printing different contents on template documents, e.g., such as statements or bills, a sheet on which a template portion is printed in advance (hereinafter, referred to as a preprint sheet) is prepared. To the preprint sheet, specific information (hereinafter, referred to as a variable image) unique to each individual document, such as the address and amount of the bill, is individually printed. This printing method is referred to as the preprint printing.
In order to inspect the printed matter which is preprint-printed, a master image is generated for each specific document and corresponding portions of the master image and an inspection image are compared to determine, by the degree of the difference therebetween, whether there is a defect in the printed matter. However, in such a method, since the master image does not include information on a content (preprint image) printed on the preprint sheet, the inspection apparatus detects such content (preprint image) as the difference between the inspection image and the master image such that an accurate result is not obtained.
In view of this, Japanese Patent Application Publication No. H11-78183-A describes an inspection method, in which a preprint image layer of an inspection image is masked to generate the inspection image having only a variable image, and the inspection image is compared with a master image to inspect a defect.
Japanese Patent Application Publication No. 2005-49212-A describes an inspection method, in which change in magnification and change in print position are calculated for each of a preprint image layer and a variable image layer of an inspection image, and when the calculation result exceeds a threshold, it is determined that a print result is defective.